This application is based upon and claimed the benefit of priority from the prior Japanese Patent application NO. 2000-199937 filed on Jun. 30, 2000.
The present invention relates to a liquid process type image-forming apparatus, and more particularly, concerns a system for removing liquid carrier from a liquid developed image obtained by developing with a developer containing liquid carrier and toner particles, and a liquid process type image-forming apparatus with the aforementioned system.
Image-forming apparatus such as an electrophotographic recorder or an electrostatic recorder utilizing a liquid developer has some advantages which cannot be realized with dry type one, so that its value has been thought better lately.
Being able to obtain high quality images thanks to extremely fine toner particles of sub-micron in diameter, being able to obtain inexpensively a good image quality comparable to that of printing (e.g. offset) because sufficient image density can be obtained with a small amount of toner, and being able to accomplish energy saving because toner can be fixed to a copy sheet at a relatively low temperature, etc. are the important advantages of the liquid process type image-forming apparatus employing liquid developer over the dry process type image-forming apparatus.
On the other hand, since conventional image-forming apparatus using liquid developer has some essential problems, the dry process technology has held an unchallenged position for a long time. One of these problems is related to liquid carrier for liquid developer.
Because non-polarity and non-conductivity are indispensable properties for the usual liquid carrier, petrochemical material is used, which volatilizes and emanates peculiar smell. In order to reduce such smell, several methods have ever been investigated to collect the smell in liquid state as much as possible before the liquid carrier volatilizes in the image-forming apparatus.
For example, U.S. Pat. Nos. 5,873,014 and 5,978,630 disclose a method to absorb and collect excess liquid carrier of a liquid developed image by contacting a cylindrical porous roller (inside of which is evacuated to be in sucking condition at its surface.) to a surface of an electrostatic latent image bearing member, on which the liquid developed image obtained by developing is formed.
On the other hand, it is required to remove and collect such liquid carrier without disturbing a visible image formed by toner particles on the surface of the latent image bearing member, or without exfoliating the toner particles from the latent image forming surface.
For example, in the method to remove and collect the liquid carrier mentioned above, disturbance of the visible image and exfoliation of the toner particles are prevented by preparing a part of the porous roller with conductive material and giving the porous roller a bias voltage to keep off the toner particles.
However, sucking up the excess liquid carrier of the liquid developed image by a negative pressure makes the sucking force difficult to control, and then proper range of sucking becomes narrow. Therefore when the sucking force by a vacuum pump is raised to collect quickly the liquid carrier absorbed in the porous material, not only the liquid carrier absorbed in the porous material but also the toner particles forming the visible image on the electrostatic latent image forming surface are exfoliated. The inventors have realized that the roller cannot bear operation for a long period by this method, because the exfoliated toner particles clog up the fine pores of the porous roller. U.S. Pat. No. 5,873,014 discloses an idea to blow off above-mentioned clogging using a positive pressure.
Furthermore, when multicolor images are formed by means of Image on image"" method in which a second color visible image is formed in layers on a first color visible image after the first color visible image has been formed, the toner particles forming the second color image are selectively taken off because developing adhesive force of the particles differs from that of the first color particles if the aforementioned collection/removing method for the liquid carrier is adopted, and consequently the problem that a desirable color cannot be created takes place.
As mentioned above, in the conventional liquid process type image-forming apparatus, there have been some problems that the liquid developed image is disturbed when the excess liquid carrier is removed, and the roller cannot bear a long period operation.
In accordance with an aspect of the present invention, an liquid carrier removing system for removing at least a part of liquid carrier from a liquid developed image formed with toner particles dispersed in the liquid carrier and adhered by electrophoresis to an electrostatic latent image on an image forming surface movable in a predetermined direction, the system comprising:
an absorbing cylinder being pressed by a portion of the image forming surface on which the liquid developed image is formed, and absorbing at least a part of the liquid carrier on the portion when the portion is released from the pressed condition as the image forming surface moves, wherein the absorbing cylinder has a porous core and an elastic porous layer formed on the porous core;
a vacuum system coupled to the absorbing cylinder, which collects the liquid carrier absorbed in the elastic porous layer into an inner side of the absorbing cylinder with generation of a negative pressure; and
a shield arranged at the inner side of the absorbing cylinder and fixed at least a region corresponding to the pressed portion for preventing an air flow caused by the negative pressure from flowing into said cylinder.
Furthermore, in accordance with another aspect of the present invention, an image-forming apparatus comprises:
an electrostatic latent image bearing member having a cylindrical electrostatic latent image forming surface;
at least one of a plurality of stages, the stage including a charger located around said electrostatic latent image forming surface for charging said forming surface, an exposure apparatus which forms the electrostatic latent image on the charged forming surface, a developer unit which develops the electrostatic latent image with toner particles dispersed in liquid carrier into a liquid developed image, and a squeeze roller which exfoliates a part of the liquid carrier of the liquid developed image;
a liquid carrier removing apparatus containing:
an absorbing cylinder being elastically pressed by a portion of the forming surface on which the liquid developed image through the squeeze roller is formed and absorbing at least a part of the liquid carrier on said portion when the portion is released from the pressed condition as said forming surface moves, wherein said absorbing cylinder has a porous core and an elastic porous layer formed on the porous core,
a vacuum system coupled to the absorbing cylinder, which collects at least a part of the liquid carrier absorbed in the elastic porous layer into an inner side of the absorbing cylinder with generation of a negative pressure; and
a shield arranged at the inner side of the absorbing cylinder and fixed at least a region corresponding to the pressed portion for preventing an air flow caused by the negative pressure from flowing into the cylinder; and
a transferring system which transfers the liquid developed image via the liquid carrier removing apparatus to a medium.
In accordance with the aspect of the present invention, thanks to the presence of the shield, the liquid carrier is removed only by a sucking force of the porous body, even though the inside of the porous cylinder is decompressed. As the liquid carrier absorbed in the porous body is sucked inside the cylinder by decompressing the inside of the porous cylinder, collecting capability for the liquid carrier recovers when the cylinder rotates in the porous body and then contacts the liquid carrier on the surface of the latent image bearing member.